A conventional method of preparing 1,4-cyclohexanedimethanol may be categorized into two methods. One method is a method of synthesizing 1,4-cyclohexanedimethanol through 1,4-dimethyl cyclohexane dicarboxylate under high-temperature and high-pressure conditions using dimethyl terephthalate, and the other method is a method of synthesizing 1,4-cyclohexanedicarboxylic acid using terephthalic acid and preparing 1,4-cyclohexanedimethanol therefrom.
However, the previously known methods of preparing 1,4-cyclohexanedimethanol may be uneconomical in that an additional process for removing or recovering by-products generated during process commercialization or catalysts used in each step may be required. Thus, there is a need to develop an efficient method which compensates these limitations by simplifying a reaction process, prepares 1,4-cyclohexanedimethanol from terephthalic acid which is known that hydrogenation is difficult, and simultaneously reduces reaction time and by-products.
The present invention is a technique of preparing 1,4-cyclohexanedimethanol from terephthalic acid in a sequential manner using a hydrogenation catalyst in a single reactor, wherein there is no direct prior art, but some prior arts are summarized as follows.
Japanese Patent Application Laid-Open Publication No. 2002-145824 discloses a method of preparing 1,4-cyclohexanedimethanol in which terephthalic acid is hydrogenated in the presence of a solvent and a palladium catalyst, 1,4-cyclohexanedimethanol, as an intermediate, is obtained, and hydrogenation is then further performed thereon. However, by-products are generated in this method to reduce selectivity of the finally prepared 1,4-cyclohexanedimethanol, and accordingly, it is disadvantageous in that higher aliphatic alcohol, such as 2-ethylhexanol, is used as an extraction agent or processes of separating and recovering the generated by-products and alcohol are required.
European Patent No. 0934920 discloses a preparation method in which a Raney catalyst is prepared to reduce terephthalic acid, but, since this method uses the catalyst, which is not easy to be commercialized in a large scale, and uses dioxane as well as water as a reaction solvent, separation and recovery processes for each component may be required. Thus, its application area may be limited.
U.S. Pat. No. 6,294,703 discloses a method of synthesizing 1,4-cyclohexanedimethanol from 1,4-cyclohexanedicarboxylic acid using a composite catalyst impregnated with ruthenium and tin, but it is difficult to sufficiently secure the selectivity of the finally prepared 1,4-cyclohexanedimethanol and, since a base must be used during hydrogenation, a separate and additional process or cost for processing the base in a commercialization process may be required and environmental problems may also occur.
With respect to a conventional method of preparing 1,4-cyclohexanedimethanol, purity or reaction efficiency of the finally obtained 1,4-cyclohexanedimethanol is not very high. Also, since solubility of terephthalic acid among reactants in water is low, a salt of metal, such as alkali metal, must be prepared and reacted to increase reactivity when water is used as a solvent. Thus, in order to obtain trans-1,4-cyclohexanedimethanol as a final product, it is inconvenient that the metal of the metal salt must be substituted with a hydrogen ion by an acid treatment. Furthermore, in cis/trans-mixed-1,4-cyclohexanedimethanol, caution is required because there is a tendency that the higher the ratio of the trans-1,4-cyclohexanedimethanol is, the more the dissolution temperature in water, as the solvent, increases.
Korean Patent No. 1073067 discloses a technique in which dimethyl 1,4-cyclohexane dicarboxylate (DMCD) is used as a raw material and 1,4-cyclohexanedicarboxylic acid (CHDA) is prepared and recrystallized by hydrolysis in a solvent, but, since an ion exchange resin, in which a restrictive reaction condition is disadvantageous, and an acid catalyst, such as paratoluenesulfonic acid (p-TSA), are used, neutralization equipment and process may be additionally required.
Japanese Patent No. 4513256 discloses a technique in which cis-1,4-cyclohexanedicarboxylic acid (c-CHDA) is heated at a melting point of 300° C. or more and then crystallized to be precipitated into trans-1,4-cyclohexanedicarboxylic acid (t-CHDA), but, when the above condition is commercialized, it is inconvenient that the high temperature must be maintained for 1 hour or more, and purification/separation equipment may be required.
Japanese Patent Application Laid-Open Publication No. 2010-270093 discloses a method of preparing trans-1,4-cyclohexanedicarboxylic acid dimethyl (HDMT) from cis/trans mixed-1,4-cyclohexanedicarboxylic acid dimethyl by processes I and II using a catalyst, but the HDMT is a material for preparing trans-1,4-cyclohexanedicarboxylic acid (t-CHDA), wherein process equipment must be additionally installed in comparison to the known method, and separate neutralization equipment may be required due to base catalysis.
Non-Patent Document 1 (Journal of Organic Chemistry, 31(10), 3438-9, 1996) discloses a method in which terephthalic acid is hydrogenated in an aqueous solution in the presence of a rhodium and alumina catalyst under conditions including a temperature of 60° C. to 70° C. and a hydrogen pressure of 3 kg/cm2 or less, the obtained reactant is extracted with chloroform after the catalyst is removed from the reactant by high-temperature filtration, and 1,4-cyclohexanedimethanol is obtained in a yield of 90%, but, since the chloroform is used as an extraction solution after the reaction, environmental issues are generated and additional recovery equipment is required, and thus, there is a limitation in using the method.
Non-Patent Document 2 (Applied Catalysis A: General 154 (1997) 75-86) discloses a method of obtaining 90% or more of 1,4-cyclohexanedimethanol at 230° C. and 100 kg/cm2 using Ru—Sn metal, but, since there is a disadvantageous in that a yield of cyclohexanedimethanol is rapidly decreased when the number of reuses of the catalyst is greater than 5 times, its practical application may be difficult.
Non-Patent Document 3 (Chem. Eur J. 2009, 15, 6953-6963) discloses a method of obtaining 1,4-cyclohexanedicarboxylic acid by reacting terephthalic acid at 60° C. and 100 kg/cm2 for 24 hours using a ruthenium catalyst, but, since the reaction time is excessively long and lithium aluminum hydride (LiAlH4), as an alkali metal in which commercialization of the process is difficult, is used, its application may be difficult.